The changes are already reverted (DEV: Revert topic loading async changes by CvX · Pull Request #18757 · discourse/discourse · GitHub) but haven’t landed on tests-passed branch yet because of the issues in our internal CI process. Should be up within an hour.
update: the revert is now on tests-passed
To be able to reproduce the issue consistently it’s required to either use a slower device (or a device under heavy load) or under worse network conditions. That’s why mobile could be more affected more often.